Robust nCuO modulated by defect engineering enhanced photoelectrochemical biosensor for the detection of miRNA-21

Traditional p-type CuO (pCuO), valued for its tunable band gap and p-type conductivity, has been widely used in photoelectrochemical biosensors. However, its weak conductivity leads to unsatisfied photoelectrochemical signals and limits its use in in situ vulcanization reactions. We synthesized n-type CuO (nCuO) with abundant oxygen vacancies through a simple chemical reduction for the first time, which was applied as efficient photoactive material. The resulting nCuO exhibits superior photoelectrochemical performance than pCuO, thanks to enhanced carrier separation facilitated by the oxygen vacancies. Upon miRNA-21 introduction, H₂S was generated, which can react with Cu(II) to form nCuO-pCuS heterojunction on the electrode. Inspiringly, the current increase of nCuO is 2.3 times higher than the pCuO after vulcanization reaction due to the built-in electric field of the nCuO-pCuS heterojunction can promote efficient carrier separation. Under optimal conditions, the biosensor offers excellent analytical performance, with a wide linear range (0.004–400 pM) and a detection limit of 1.8 fM. The integration of oxygen defect engineering and target-triggered vulcanization presents a new strategy for designing high-performance photoelectrochemical biosensors.